This study was carried out on a real site of a gymnasium situated in t
he centre of France. The building is equipped with two remarkable ener
gy saving devices running together : a ventilated roof and an air-eart
h heat exchanger. Experimental and theoretical studies were done on th
ese two energy saving systems and a sensitivity factor analysis was pe
rformed. First, each component was modelled in order to (1) determine
the component's contribution to the energy savings; and (2) indicate t
he relative importance of different types of heat transfer which occur
in the ventilated roof Then, several types of fresh air preheating we
re studied, varying the heating control temperature of the building. T
he main results show that the economic of fresh air preheating can var
y with the system used, and indicate the reasons for the lack of effic
iency of some systems. Finally, fresh air introduction into the gymnas
ium was optimized. The combined influences of ventilation intermittenc
y and climate on the global theoretical consumptions for the building
were studied. It was shown that the optimization of air introduction i
nto the gymnasium has no influence on the energy consumption of the bu
ilding for a rather cold climate. On the other hand, for a warmer clim
ate, significant energy savings can be obtained. In conclusion, this s
tudy points out the general interest of simulation for nee building de
signs. However, it can be also used for existing buildings to give sig
nificant information about equipment weaknesses and, of course, about
improvements to be made. (C) 1997 Elsevier Science Ltd.